Linear compressor

ABSTRACT

A linear compressor is provided that may include a shell including a refrigerant inlet, an outer stator provided in the shell and including a coil, an inner stator disposed to be spaced apart from the outer stator, a permanent magnet disposed to be movable between the outer stator and the inner stator, a cylinder including a compression space, in which a refrigerant sucked in through refrigerant inlet may be compressed, a piston coupled to the permanent magnet so as to be reciprocated in the cylinder, a first surface area provided on the piston and having a first hardness value, and a second surface area provided on the cylinder and having a second hardness value, such that a difference value between the first and second hardness values is more than a preset value.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 10-2013-0075514, filed in Korea on Jun. 28, 2013, which is hereby incorporated by reference in its entirety.

BACKGROUND

1. Field

A linear compressor is disclosed herein.

2. Background

In general, compressors may be mechanisms that receive power from power generation devices, such as electric motors or turbines, to compress air, refrigerants, or other working gases, thereby increasing a pressure of the working gas. Compressors are widely used in home appliances or industrial machineries, such as refrigerators and air-conditioners.

Compressors may be largely classified into reciprocating compressors, in which a compression space, into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between a piston and a cylinder to compress the refrigerant while the piston is linearly reciprocated within the cylinder; rotary compressors, in which a compression space into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between a roller, which is eccentrically rotated, and a cylinder to compress the refrigerant while the roller is eccentrically rotated along an inner wall of the cylinder; and scroll compressors, in which a compression space, into and from which a working gas, such as a refrigerant, is suctioned and discharged, is defined between an orbiting scroll and a fixed scroll to compress the refrigerant while the orbiting scroll is rotated along the fixed scroll. In recent years, among the reciprocating compressors, linear compressors having a simple structure in which a piston is directly connected to a drive motor, which is linearly reciprocated, to improve compression efficiency without mechanical loss due to switching in moving, are being actively developed. Generally, such a linear compressor is configured to suction and compress a refrigerant while a piston is linearly reciprocated within a cylinder by a linear motor in a sealed shell, thereby discharging the compressed refrigerant.

The linear motor has a structure in which a permanent magnet is disposed between an inner stator and an outer stator. The permanent magnet may be linearly reciprocated by a mutual electromagnetic force between the permanent magnet and the inner (or outer) stator. Also, as the permanent magnet is operated in a state in which the permanent magnet is connected to the piston, the refrigerant may be suctioned and compressed while the piston is linearly reciprocated within the cylinder and then be discharged.

A linear compressor according to the related art is disclosed in Korean Patent Publication No. 10-2010-0010421. According to the related art, while the piston repeatedly moves within the cylinder, interference between the cylinder and the piston may occur causing abrasion of the cylinder or piston. More particularly, when a predetermined pressure (a coupling pressure) acts on the piston causing deformation of the piston due to the pressure, interference between the cylinder and the piston may occur. Also, if a slight error occurs when the piston is assembled with the cylinder, a compression gas may leak to the outside, and thus, abrasion between the cylinder and the piston may occur.

As described above, the interference between the cylinder and the piston may occur causing interference between the permanent magnet and the inner and outer stators, thereby damaging components. Also, in the case of the linear compressor according to the related art, the cylinder and/or the piston may be formed of a magnetic material. Thus, a large amount of flux generated in the linear motor may leak to the outside through the cylinder and the piston, deteriorating efficiency of the compressor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described in detail with reference to the following drawings in which like reference numerals refer to like elements, and wherein:

FIG. 1 is a cross-sectional view of a linear compressor in accordance with an embodiment;

FIG. 2 is a cross-sectional view illustrating a coupling state between a cylinder and a piston according to an embodiment;

FIG. 3 is a cross-sectional view illustrating a state in which the piston of FIG. 2 is moved in one direction;

FIG. 4 is a cross-sectional view illustrating a state in which a piston and a cylinder are coupled with each other according to an embodiment; and

FIG. 5 is a graph illustrating change in abrasion ratio of the cylinder or the piston according to a difference in hardness between first and second surface areas according to an embodiment.

DETAILED DESCRIPTION

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Embodiments may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, alternate embodiments included in other retrogressive inventions or falling within the spirit and scope of the present disclosure can easily be derived through adding, altering, and changing, and will fully convey the concept of the invention to those skilled in the art.

FIG. 1 is a cross-sectional view of a linear compressor in accordance with an embodiment. Referring to FIG. 1, the linear compressor 10 may include a cylinder 120 disposed in a shell 100, a piston 130 that linearly reciprocates in the cylinder 120, and a motor assembly 200 that provides a drive force to the piston 130. The shell 100 may include an upper shell and a lower shell.

The shell 100 may further include an inlet 101, through which a refrigerant may flow into the shell 100, and an outlet 105, through which the refrigerant compressed in the cylinder 120 may be discharged from the shell 100. The refrigerant sucked in through the inlet 101 may flow into the piston 130 through a suction muffler 140. While the refrigerant passes through the suction muffler 140, noise may be reduced.

A compression space P, in which the refrigerant may be compressed by the piston 130, may be provided in the cylinder 120. A suction hole 131 a, through which the refrigerant may be introduced to the compression space P, may be provided at the piston 130, and a suction valve 132 may be provided at a side of the suction hole 131 a to selectively open the suction hole 131 a.

A discharge valve assembly 170, 172, and 174 may be provided at a side of the compression space P to discharge the refrigerant compressed in the compression space P. That is, the compression space P may be defined between an end of the piston 130 and the discharge valve assembly 170, 172, and 174.

The discharge valve assembly 170, 172, 174 may include a discharge cover 172, which may define a discharge space for the refrigerant, a discharge valve 170, which may be opened so that the refrigerant may be introduced into the discharge space when a pressure of the compression space P is more than a discharge pressure, and a valve spring 174, which may be provided between the discharge valve 170 and the discharge cover 172 so as to provide an elastic force in an axial direction. The term “axial direction” may refer to a reciprocating direction of the piston 130, that is, a transverse direction in FIG. 1. The suction valve 132 may be provided at a first side of the compression space P, and the discharge valve 170 may be provided at a second side of the compression space P, that is, at an opposite side to the suction valve 132.

While the piston 130 is reciprocated in the cylinder 120, if the pressure of the compression space P is lower than the discharge pressure and also less than a suction pressure, the suction valve 132 may be opened, and the refrigerant may be suctioned into the compression space P. On the other hand, if the pressure of the compression space P is more than the suction pressure, the suction valve 132 may be closed and the refrigerant in the compression space P compressed. If the pressure of the compression space P is more than the discharge pressure, the valve spring 174 may be deformed so as to open the discharge valve 170, and the refrigerant discharged from the compression space P to the discharge space of the discharge cover 172.

The refrigerant in the discharge space may be introduced into a loop pipe 178 through a discharge muffler 176. The discharge muffler 176 may reduce a flow noise of the compressed refrigerant, and the loop pipe 178 may guide the compressed refrigerant to the outlet 105. The loop pipe 178 may be coupled to the discharge muffler 176 and curvedly extended to be coupled to the outlet 105.

The linear compressor 10 may further include a frame 110. The frame 110 may serve to fix the cylinder 200 within the shell 100. The frame 110 may be integrally provided with the cylinder 200 or may be fastened to the cylinder 200 by a separated fastening member, for example. The discharge cover 172 and the discharge muffler 176 may be coupled to the frame 110.

The motor assembly 200 may include an outer stator 210, which may be fixed to the frame 110 and disposed to enclose or surround the cylinder 120, an inner stator 220, which may be disposed inside the outer stator 210 to be spaced apart from the outer stator 210, and a permanent magnet 230, which may be disposed at or in a space between the outer and inner stators 210 and 220. The permanent magnet 230 may be linearly reciprocated by an electromagnetic force between the outer and inner stators 210 and 220. Further, the permanent magnet 230 may be a single magnet having one pole, or may be formed by coupling a plurality of magnets having three poles. More specifically, in a case of the permanent magnet 230 having three poles, one surface thereof may have a polar distribution of a N-S-N type, and the other surface thereof may have a polar distribution of a S-N-S type.

The permanent magnet 230 may be coupled to the piston 130 by a connection member 138. The connection member 138 may extend from an end of the piston 130 to the permanent magnet 130. As the permanent magnet 230 is linearly moved, the piston 130 may be linearly reciprocated together with the permanent magnet 230 in the axial direction.

The outer stator 210 may include a bobbin 213, a coil 215, and a stator core 211. The coil 215 may be wound in a circumferential direction of the bobbin 213. The coil 215 may have a polygonal shape, for example, a hexagonal shape. The stator core 211 may be configured by stacking a plurality of laminations in the circumferential direction, and may be disposed so as to enclose the bobbin 213 and the coil 215.

If a current is applied to the motor assembly 200, the current may flow through the coil 215, and a magnetic flux may be generated around the coil 215. The magnetic flux may form a closed circuit and flow along the outer and inner stators 210 and 220. The magnetic flux flowing along the outer and inner stators 210 and 220 may interact with a magnetic flux of the permanent magnet 230, and thus, a force to move the permanent magnet 230 may be generated.

A stator cover 240 may be provided at a side of the outer stator 210. A first side end of the outer stator 210 may be supported by the frame 110, and a second side end thereof may be supported by the stator cover 240.

The inner stator 220 may be fixed to an outer circumference of the cylinder 120. The inner stator 220 may be configured by stacking a plurality of laminations in a circumferential direction at an outside of the cylinder 120.

The linear compressor 10 may further include a supporter 135 that supports the piston 130, and a back cover 115 that extends from the piston 130 toward the inlet 101. The back cover 115 may be disposed so as to cover at least a portion of the suction muffler 140.

The linear compressor 10 may include a plurality of springs 151 and 155, a natural frequency of which may be controlled so as to enable a resonant motion of the piston 130. The plurality of springs 151 and 155 may include a plurality of first springs 151, which may be disposed between the supporter 135 and the stator cover 240, and a plurality of second springs 155, which may be disposed between the supporter 135 and the back cover 115.

The plurality of first springs 151 may be provided at both sides of the cylinder 120 or the piston 130, and the plurality of second springs 155 may be provided at a front side of the cylinder 120 or the piston 130. The term a “front side” may refer to a direction from the piston 130 toward the inlet 101. The term a “rear side” may refer to a direction from the inlet 101 toward the discharge valve assembly 170, 172, and 174. These terms may also be used in the below description.

A predetermined amount of oil may be stored at or in an internal bottom surface of the shell 100, and an oil supplying device 160 may be provided at a lower side of the shell 100 to pump the oil. The oil supplying device 160 may be operated by vibration generated when the piston 130 is linearly reciprocated, so as to pump the oil upwardly.

The linear compressor 10 may further include an oil supply pipe 165 that guides oil flow from the oil supplying device 160. The oil supply pipe 165 may extend from the oil supplying device 160 to a space between the cylinder 120 and the piston 130. The oil pumped from the oil supplying device 160 may be supplied to the space between the cylinder 120 and the piston through the oil supply pipe 165, and perform cooling and lubricating functions.

FIG. 2 is a cross-sectional view illustrating a coupling state between a cylinder and a piston according to an embodiment. FIG. 3 is a cross-sectional view illustrating a state in which the piston of FIG. 2 is moved in one direction. FIG. 4 is a cross-sectional view illustrating a state in which a piston and a cylinder are coupled with each other according to an embodiment.

Referring to FIGS. 2 to 4, the piston 130 according to this embodiment may be provided in the cylinder 120 to be reciprocated. The piston 130 may be made of an aluminum material, for example, aluminum or an aluminum alloy, which is a non-magnetic material. As the piston 130 may be made of the aluminum material, magnetic flux generated at the motor assembly 200 may be prevented from being transferred to the piston 130 and then leaked to an outside of the piston 130. The piston 130 may be formed by forging, for example.

The piston 130 may include a piston body 131, which may have an approximately cylindrical shape and may be disposed in the cylinder 120, and a flange 136, which may be radially expanded from a side end of the piston body 131 and coupled to the permanent magnet 230.

The inlet 131 a may be provided at a first surface of the piston body 131. The first surface of the piston body 131 may be a surface facing the discharge valve 170, for example, a rear surface thereof.

The piston body 131 may include an outer circumferential surface on which a first surface area 310, which may be in the form of a predetermined layer or film, may be provided. The first surface area 310 may be provided on the outer circumferential surface of the piston body 131 in a surface treatment manner. By providing the first surface area 310, it is possible to improve abrasion resistance, lubricity, and heat resistance of the piston body 131. For example, the first surface area 310 may be a “first coating layer”. For example, the first surface area 310 may be made of one of polytera fluoroethylene (PTFE), diamond like carbon (DLC), a nickel-phosphorus alloy, or an anodizing layer.

The flange 136 may include a plurality of holes 137 a and 137 b. The plurality of holes 137 a and 137 b may include one or more coupling holes 137 a, in which a fastening member coupled with the supporter 135 and the connection member 138 may be inserted, and one or more through-holes 137 b, which may reduce flow resistance generated around the piston 130.

The cylinder 120 may be made of an aluminum material, for example, aluminum or an aluminum alloy, which is a non-magnetic material. A material composition ratio, that is, a kind and composition of the material in each of the cylinder 120 and the piston 130 may be the same.

As the cylinder 120 may be made of the aluminum material, magnetic flux generated at the motor assembly 200 may be prevented from being transferred to the cylinder 120 and then leaked to an outside of the cylinder 120. Further, the cylinder 120 may be formed by extruded rod processing, for example.

As the piston 130 and the cylinder 120 may be made of the same material, for example, aluminum, the piston 130 and the cylinder 120 may have a same thermal expansion coefficient. While the linear compressor 10 is operated, a high temperature environment approximately (100° C.) is created in the shell 100. As the piston 130 and the cylinder 120 have the same thermal expansion coefficient, the piston 130 and the cylinder 120 may be equally thermally deformed. As the piston 130 and the cylinder 120 may be thermally deformed in different sizes or directions, the piston 130 may be prevented from interfering with the cylinder 120, while the piston 130 is reciprocated.

The cylinder 120 may have the hollow cylindrical shape, and the piston body 131 may be movably received therein. The cylinder 120 may include an inner circumferential surface disposed opposite to an outer circumferential surface of the piston body 131. A second surface area 320, which may be in the form of a predetermined layer or film, may be provided on the inner circumferential surface of the cylinder 120.

The second surface area 320 may be provided using a different surface treatment from that of the first surface area 310. By providing the second surface area 320, it is possible to improve abrasion resistance, lubricity, and heat resistance of the piston body 131. For example, the second surface area 320 may be a “second coating layer”. For example, the second surface area 320 may be made of one of Teflon (PTFE), diamond like carbon (DLC), a nickel-phosphorus alloy, or a anodizing layer.

A certain difference in hardness between the outer circumferential surface of the piston 130 and the inner circumferential surface of the cylinder 120 may be generated. If the difference in hardness therebetween is too small, one of the piston 130 or the cylinder 120 may be stuck to the other one, that is, the surface thereof may be worn, while the piston 130 is reciprocated in the cylinder 120.

Therefore, in this embodiment, each of the piston 130 having the first surface area 310 and the cylinder 120 having the second surface area 320 may have a hardness greater than a predetermined value, and thus, the abrasion resistance of the piston 130 and the cylinder 120 may be improved.

Hereinafter, a surface area treatment method for the first surface area 310 or the second surface area 320 will be described.

The first surface area 310 or the second surface area 320 may include polytera fluoroethylene (PTFE). PTFE is a fluorinate polymer, which is referred to as “Teflon”.

In a state in which the fluorinate polymer is formed into a paint, the PTFE may be sprayed on the outer circumferential surface of the piston 130 or the inner circumferential surface of the cylinder 120, and treated by heating and plastic working at a predetermined temperature, thereby providing an inactive coating layer. As the PTFE has a low frictional coefficient, the PTFE may be coated on the outer circumferential surface of the piston 130 or the inner circumferential surface of the cylinder 120, to enhance lubricity and abrasion resistance of the surface.

The hardness of the PTFE is very small, and may be measured by a measuring method of pencil hardness. For example, the hardness of the PTFE may be more than a pencil hardness of HB. However, when the hardness of the PTFE is converted into Vickers hardness (Hv), the PTFE may have approximately 0 to approximately 30Hv (referring to Table 1).

For example, the first surface area 310 or the second surface area 320 may include a film prepared by an anodizing technique, that is, an anodizing layer. The anodizing technique is a kind of aluminum painting, in which, when current is applied in a state in which aluminum is used as an anode, an aluminum surface is oxidized by oxygen generated at the anode, and thus, an oxidized aluminum layer is provided.

The anodizing layer has excellent corrosion resistance and electrical breakdown resistance. The hardness of the anodizing layer may be changed according to a state or a composition of a material (a basic material) to be coated, and may be approximately 300 to 500Hv (referring to Table 1).

As another example, the first surface area 310 or the second surface area 320 may include diamond-like carbon (DLC). DLC is an amorphous carbon-based new material which is a thin film-shaped material prepared by electrically accelerating carbon ions in plasma or activated hydrocarbon molecules and smashing them on the surface. DLC has similar physical properties to diamond, and thus, has high hardness and abrasion resistance, excellent electrical breakdown resistance, a low frictional coefficient, and excellent lubricity. The hardness of the DLC may be approximately 1,500 to 1,800 (referring to Table 1).

As still another example, the first surface area 310 or the second surface area 320 may include a nickel-phosphorus alloy material. The nickel-phosphorus alloy material may be provided on the outer circumferential surface of the piston 130 or the inner circumferential surface of the cylinder 120 by an electroless nickel plating manner, such that nickel and phosphorus are surface-segregated in a uniform thickness. The nickel-phosphorus alloy material may have a chemical composition in which nickel content is approximately 90 to 92%, phosphorus content is approximately 9 to 10%.

The nickel-phosphorus alloy material may improve corrosion resistance and abrasion resistance of the surface and also provide excellent lubricity. The hardness of the nickel-phosphorus alloy material may be approximately 500 to 600Hv. (referring to Table 1).

TABLE 1 Coating material (method) Hardness (Hv, Vickers hardness) PTFE (Teflon)  0~30 (average: 15) Anodizing layer 300~500 (average: 400) DLC (Diamond-Like Carbon) 1,500~1,800 (average: 1,650)   Ni—P alloy 500~600 (average: 550)

As described above, the first surface area 310 or the second surface area 320 may be provided by one of the four coating materials (methods), for example.

However, the first surface area 310 and the second surface area 320 may be provided by different coating materials (methods) from each other. Therefore, the outer circumferential surface of the piston 130 and the inner circumferential surface of the cylinder 120 may have a hardness difference, which is more than a predetermined value. For convenience of explanation, a hardness valve of the first surface area 310 may be referred to as a “first hardness value”, and a hardness value of the second surface area 320 may be referred to as a “second hardness value”.

In this embodiment, the above four materials (methods) may be selected to provide the hardness difference which is more than the predetermined value. Hereinafter, referring to an experimental graph, a change in an abrasion ratio of the cylinder or the piston according to the hardness difference between the first and second surface areas will be described.

FIG. 5 is a graph illustrating change in abrasion ratio of the cylinder or the piston according to a hardness difference between first and second surface areas in accordance with an embodiment. In FIG. 5, a predetermined surface area was provided on each of the outer circumferential surface of the piston 130 and the inner circumferential surface of the cylinder 120, and an abrasion ratio occurring at the piston or the cylinder according to a hardness difference between surface area was experimentally measured and organized. The predetermined surface area was prepared using various materials or methods other than the four methods described in Table 1. While the piston 130 was repeatedly reciprocated in the cylinder 120, it was targeted to maintain the abrasion ratio of the surface of the piston 130 or the cylinder 120 at approximately 3 μm or less in order to prevent damage to the piston 130 and the cylinder 120 and to secure operation reliability.

Referring to FIG. 5, the surface areas were provided so that the hardness difference between the first surface area 310 of the piston 130 and the second surface area 320 of the cylinder 120 was approximately 50Hv, and then, for example, reciprocation of the piston 130 was performed for approximately 100 hours or more. In this case, the abrasion ratio of the piston 130 or the cylinder 120 was approximately 5 μm

When the hardness difference between the first surface area 310 and the second surface area 320 was approximately 80Hv, the abrasion ratio of the piston 130 or the cylinder 120 was approximately 4 μm. When the hardness difference between the first surface area 310 and the second surface area 320 was P1, the abrasion ratio of the piston 130 or the cylinder 120 was approximately 3 μm. P1 is formed around approximately 150Hv. In a range in which the hardness difference is P1 or more, the abrasion ratio is maintained at 3 μm or less. As the hardness difference is increased, the abrasion ratio may be gradually decreased. In other words, in order to secure operation reliability of the piston 130 and the cylinder 120, each surface treatment or area may be selected so that the hardness difference between the first surface area 310 of the piston 130 and the second surface area 320 of the cylinder 120 is approximately 150Hv or more.

Hereinafter, referring to Table 2, when one of the four coating materials (methods) is provided on the first surface area 310 of the piston 130 and another one is provided on the second surface area 320 of the cylinder 120, the hardness difference of the piston 130 and the cylinder 120 may be described as follows.

TABLE 2 Hardness difference (Hv) First surface area Second surface area between surface areas PTFE (Teflon) Anodizing layer 385 DLC 1,635 Ni—P alloy 535 Anodizing layer PTFE 385 DLC 1,250 Ni—P alloy 150 DLC (Diamond- PTFE 1,635 Like Carbon) Anodizing layer 1,250 Ni—P alloy 1,100 Ni—P alloy PTFE 535 Anodizing layer 150 DLC 1,100

Table 2 shows hardness difference values calculated by using an average hardness value of each coating material. More specifically, when the anodizing layer is provided at or on one of the first surface area 310 or the second surface area 320, and the Ni—P alloy is provided at or on the other one, the hardness difference is approximately 150Hv. However, when the DLC is provided at or on one of the first surface area 310 or the second surface area 320, and the PTFE is provided at or on the other one, the hardness difference is approximately 1,635Hv.

When the PTFE is provided at or on one of the first surface area 310 or the second surface area 320, and the anodizing layer is provided at or on the other one, the hardness difference is approximately 385Hv. When the PTFE is provided at or on one of the first surface area 310 or the second surface area 320, and the Ni—P alloy is provided at or on the other one, the hardness difference is approximately 535Hv.

When the anodizing layer is provided at or on one of the first surface area 310 and the second surface area 320, and the DLC is provided at the other one, the hardness difference is approximately 1,250Hv. When the DLC is provided at or on one of the first surface area 310 and the second surface area 320, and the Ni—P alloy is provided at the other one, the hardness difference is approximately 1,100Hv.

As described above, when the anodizing layer is provided at or on one of the first surface area 310 and the second surface area 320, and the Ni—P alloy is provided at the other one, the hardness difference value between the piston 130 and the cylinder 120 is approximately minimum 150Hv and approximately maximum 1,635Hv. That is, the hardness difference value may be at least approximately 150Hv or more.

When the first and second surface areas 310 and 320 are prepared using the above-mentioned four coating materials, the hardness difference, which is a reference for determining abrasion resistance, may be maintained at approximately 150Hv or more. In other words, when the surface treatment or area is provided on each of the outer circumferential surface of the piston 130 and the inner circumferential surface of the cylinder 120 using the four coating materials, abrasion resistance of the piston 130 or the cylinder 120 may be maintained at a predetermined level. Therefore, during reciprocation of the piston 130, it is possible to secure operation reliability of the piston 130 or the cylinder 120.

For example, when the PTFE is provided at or on the first surface area 310 of the piston 130 and the anodizing layer is provided at or on the second surface area 320 of the cylinder 120, the hardness difference between the first and second surface areas 310 and 320 may be approximately 385Hv, and thus, it is possible to satisfy the required hardness difference value.

Further, for example, the hardness difference between the first and second surface areas 310 and 320 may be approximately 150 to 385Hv, approximately 150 to 535Hv, approximately 150 to 1,100Hv, approximately 150 to 1250Hv, or approximately 150 to approximately 1,635Hv.

The PTFE coating layer may be provided on the piston 130 which is reciprocated, and thus, it is possible to improve lubricity. And the anodizing layer may be provided on the cylinder 120, and thus, it is possible to improve corrosion resistance and electrical breakdown resistance, and also, it is possible to secure operation reliability of the piston 130 and the cylinder 120.

According to embodiments, as the cylinder and the piston may be made of a non-magnetic material, more particularly, an aluminum material, it is possible to prevent flux generated from the motor assembly from being leaked to the outside of the cylinder, and also, it is possible to improve efficiency of the compressor. Further, as the surface treatment or area may be provided at or on each of opposite surfaces of the piston and the cylinder, more particularly, the outer circumferential surface of the piston and the inner circumferential surface of the cylinder, it is possible to increase abrasion resistance, and thus, to improve reliability of components of the compressor.

Furthermore, as a hardness difference value between a first surface treatment or area provided on an outer circumferential surface of the piston and a second surface treatment or area provided on an inner circumferential surface of the cylinder may be provided within a predetermined range, it is possible to reduce an abrasion ratio of the cylinder or the piston. More particularly, as the difference value between the hardness of the first surface area and a hardness of the second surface area may be maintained at a predetermined value or more, it is possible to prevent the outer circumferential surface of the piston from being stuck to the inner circumferential surface of the cylinder, and thus, to prevent damage to the piston or the cylinder.

Further, as the permanent magnet provided at the motor assembly may be made of a ferrite material, which is relatively inexpensive, it is possible to reduce manufacturing costs of the compressor.

Embodiments disclosed herein provide a linear compressor that prevents abrasion or damage of internal components thereof.

Embodiments disclosed herein provide a linear compressor that may include a shell including a refrigerant inlet, an outer stator provided in the shell and including a coil, an inner stator disposed to be spaced apart from the outer stator, a permanent magnet disposed to be movable between the outer stator and the inner stator, a cylinder including a compression space in which a refrigerant sucked in through the refrigerant inlet is compressed, a piston coupled to the permanent magnet so as to be reciprocated in the cylinder, a first surface treatment part or first surface area provided at or on the piston so as to have a first hardness value, and a second surface area part or second surface treatment provide at or on the cylinder so as to have a second hardness value so that a difference value between the first and second hardness values is more than a preset value. The preset value may be at least approximately 150Hv or more based on Vickers hardness. The preset value may be determined, so that an abrasion amount generated at the piston or the cylinder, while the piston is repeatedly reciprocated for a predetermined period of time, may be approximately 3 μm or less.

The first surface treatment part or the second treatment part may be made of one of polytetra fluoroethylene (PTFE), diamond like carbon (DLC), an Ni—P alloy, and an anodizing layer. The first surface treatment part may be made of one of the PTFE, the DLC, the Ni—P alloy, and the anodizing layer, and the second treatment part may be made of another one of the PTFE, the DLC, the Ni—P alloy, and the anodizing layer, which is different from the first surface treatment part. The first surface treatment part may be made of the PTFE, and the second surface treatment part may be made of the anodizing layer.

The piston and the cylinder may be made of a non-magnetic material. The piston and the cylinder may be made of aluminum or an aluminum alloy. The aluminum or the aluminum alloy of the piston and the cylinder may be the same material.

The first surface treatment part may be provided on an outer circumferential surface of the piston. The second surface treatment part may be provided on an inner circumferential surface of the cylinder, which is opposite to the outer circumferential surface of the piston.

The piston may include a piston body received in the cylinder, and a flange part or flange expanded in a radial direction of the piston body and coupled to the permanent magnet. The first surface treatment part may be provided on an outer circumferential surface of the piston body.

Embodiments disclosed herein provide a linear compressor that may include a piston, which is reciprocated in a cylinder by a force generated by an interaction between a flux generated by a current applied to a coil and a flux of a permanent magnet, and which includes a first surface treatment part or first surface area provided on an outer circumferential surface of the piston, and a second surface treatment part or second surface area provided on an inner circumferential surface of the cylinder. A hardness value measured at the first surface treatment part and a hardness value measured at the second surface treatment part may make a preset hardness difference.

Embodiments disclosed herein provide a linear compressor that may include a shell including a refrigerant inlet, an outer stator provided in the shell and including a coil, an inner stator disposed to be spaced apart from the outer stator, a permanent magnet disposed to be movable between the outer stator and the inner stator, a cylinder including a compression space in which a refrigerant sucked in through the refrigerant inlet may be compressed, a piston coupled to the permanent magnet so as to be reciprocated in the cylinder, a polytera fluroethylene (PTFE) coating layer, which may be surface-treated on an outer circumferential surface of the piston, and an anodizing layer which may be surface-treated on an inner circumferential surface of the cylinder.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.

Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art. 

What is claimed is:
 1. A linear compressor, comprising: a shell comprising a refrigerant inlet; an outer stator provided in the shell and comprising a coil; an inner stator disposed to be spaced apart from the outer stator; a permanent magnet disposed movable between the outer stator and the inner stator; a cylinder comprising a compression space in which a refrigerant sucked in through the refrigerant inlet is compressed; a piston coupled to the permanent magnet to be reciprocated in the cylinder; a first surface area provided on the piston, the first surface area having a first hardness value; and a second surface area provided on the cylinder, the second surface area having a second hardness value, so that a difference in value between the first and second hardness values is more than a predetermined value.
 2. The linear compressor according to claim 1, wherein the predetermined value is at least approximately 150Hv or more based on Vickers hardness.
 3. The linear compressor according to claim 1, wherein the predetermined value is determined so that an abrasion amount generated at the piston or the cylinder, while the piston is repeatedly reciprocated for a predetermined period of time, is approximately 3 μm or less.
 4. The linear compressor according to claim 2, wherein the first surface area or the second surface area is made of one of polytetra fluoroethylene (PTFE), diamond like carbon (DLC), an Ni—P alloy, or an anodizing layer.
 5. The linear compressor according to claim 4, wherein the first surface area comprises one of PTFE, DLC, Ni—P alloy, or an anodizing layer, and wherein the second surface area comprises another one of PTFE, DLC, Ni—P alloy, or an anodizing layer, which is different from the first surface area.
 6. The linear compressor according to claim 5, wherein the first surface area is made of PTFE, and the second surface area is made of the anodizing layer.
 7. The linear compressor according to claim 1, wherein the piston and the cylinder are made of a non-magnetic material.
 8. The linear compressor according to claim 7, wherein the piston and the cylinder are made of aluminum or an aluminum alloy.
 9. The linear compressor according to claim 8, wherein the aluminum or the aluminum alloy of the piston and the cylinder are the same material.
 10. The linear compressor according to claim 1, wherein the first surface area is provided on an outer circumferential surface of the piston, and the second surface area is provided on an inner circumferential surface of the cylinder, which is disposed opposite to the outer circumferential surface of the piston.
 11. The linear compressor according to claim 1, wherein the piston comprises: a piston body received in the cylinder; and a flange that extends in a radial direction of the piston body and coupled to the permanent magnet, and wherein the first surface area is provided on an outer circumferential surface of the piston body.
 12. A linear compressor comprising a piston reciprocated in a cylinder by a force generated by an interaction between a magnetic flux generated by a current applied to a coil and a magnetic flux of a permanent magnet, the linear compressor comprising: a first surface area provided on an outer circumferential surface of the piston; and a second surface area provided on an inner circumferential surface of the cylinder, wherein a predetermined difference in hardness value is provided between a hardness value of the first surface area and a hardness value of the second surface area.
 13. The linear compressor according to claim 12, wherein the predetermined difference in hardness value is at least approximately 150Hv or more based on Vickers hardness.
 14. The linear compressor according to claim 12, wherein the first surface area comprises one of polytetra fluoroethylene (PTFE), diamond like carbon (DLC), an Ni—P alloy, or an anodizing layer, and the second surface area comprises another one of PTFE, DLC, Ni—P alloy, or an anodizing layer, which is different from the first surface area.
 15. A linear compressor, comprising: a shell comprising a refrigerant inlet; an outer stator provided in the shell and comprising a coil; an inner stator disposed to be spaced apart from the outer stator; a permanent magnet disposed movable between the outer stator and the inner stator; a cylinder comprising a compression space in which a refrigerant sucked in through the refrigerant inlet is compressed; a piston coupled to the permanent magnet to be reciprocated in the cylinder; a polytera fluroethylene (PTFE) layer provided on an outer circumferential surface of the piston; and an anodizing layer provided on an inner circumferential surface of the cylinder.
 16. A linear compressor, comprising: a shell comprising a refrigerant inlet; an outer stator provided in the shell and comprising a coil; an inner stator disposed to be spaced apart from the outer stator; a permanent magnet disposed movable between the outer stator and the inner stator; a cylinder comprising a compression space in which a refrigerant sucked in through the refrigerant inlet is compressed and having a first surface area having a first hardness value; and a piston coupled to the permanent magnet to be reciprocated in the cylinder and having a second surface area having a second hardness value, wherein a difference in value between the first hardness value and the second hardness value allows slippage between the cylinder and the piston.
 17. The linear compressor according to claim 16, wherein the predetermined value is at least approximately 150Hv or more based on Vickers hardness.
 18. The linear compressor according to claim 16, wherein the predetermined value is determined so that an abrasion amount generated at the piston or the cylinder, while the piston is repeatedly reciprocated for a predetermined period of time, is approximately 3 μm or less.
 19. The linear compressor according to claim 16, wherein the first surface area or the second surface area is made of one of polytetra fluoroethylene (PTFE), diamond like carbon (DLC), an Ni—P alloy, or an anodizing layer.
 20. The linear compressor according to claim 19, wherein the first surface area comprises one of PTFE, DLC, Ni—P alloy, or an anodizing layer, and wherein the second surface area comprises another one of PTFE, DLC, Ni—P alloy, or an anodizing layer, which is different from the first surface area.
 21. The linear compressor according to claim 20, wherein the first surface area is made of PTFE, and the second surface area is made of the anodizing layer.
 22. The linear compressor according to claim 16, wherein the piston and the cylinder are made of a non-magnetic material.
 23. The linear compressor according to claim 22, wherein the piston and the cylinder are made of aluminum or an aluminum alloy.
 24. The linear compressor according to claim 23, wherein the aluminum or the aluminum alloy of the piston and the cylinder are the same material. 